An organic electroluminescent (EL) device has a multilayer structure comprising (i) a luminescent layer comprising a light emitting material and (ii) a hole transport layer and an electron transport layer, which sandwich the luminescent layer, and (iii) an anode and a cathode, which sandwich the hole transport layer, the luminescent layer and the electron transport layer. The organic EL device utilizes light emission (fluorescence or phosphorescence) occurring at deactivation of an exciton formed by the recombination of electron with hole, which are injected in the luminescent layer. The organic EL device is widely used for a display and other applications.
The organic EL device is utilized in various display instruments. For utilization thereof for personal digital assistants to which supply of an electric power is restricted, it is required or eagerly desired that the power consumption is further lowered. Simultaneously, for the commercial utilization of the organic EL device, it is important to prolong the life of device with stable performances.
The 1,2,4,5-substituted phenyl compound of the present invention is characterized as having a pyridyl-substituted phenlylene group or a phenyl-substituted pyridylene group at each of 1, 2, 4 and 5 positions of a benzene ring.
Recently it has been proposed to utilize a compound having an aromatic cyclic hydrocarbon group having introduced therein bipyridyl groups, as a 1,2,4,5-substituted phenyl compound for an organic EL device in, for example, WO2009/151039. However, this patent publication is silent on a compound having pyridyl-substituted phenlylene groups or phenyl-substituted pyridylene groups on a benzene ring.
Further, it has been proposed to utilize a 1,2,4,5-substituted oligophenylene compound for an organic EL device in, for example, WO2009/081873. However, this patent publication is silent on a compound having pyridyl-substituted phenlylene groups or phenyl-substituted pyridylene groups, which are bonded to a benzene ring. Enhancement of light emission efficiency of the substituted oligophenylene compound is discussed in WO2009/081873, but, lowering of the power consumption and prolongation of the life of device are not mentioned therein.
Further, compounds having combinations of a phenyl group with a pyridyl group for use in an organic EL device have been proposed in, for example, JP2008-63232A, JP2003-336043, JP2007-015993A, JP2005-255986A and JP2008-127326A. However, these patent publications are silent on a compound having pyridyl-substituted phenlylene groups or phenyl-substituted pyridylene groups, which are bonded to a benzene ring. Organic EL devices made by using the compounds proposed in these patent publications still do not have sufficiently improved luminescent characteristics.